UToledo Researcher Uncovers Molecular Switches That Help Wire the Developing Nervous System

Reach for a coffee cup without looking at your hand. Walk downstairs while checking your phone. Touch your nose with your eyes closed. All of that is possible because of a sense most people have never heard of: proprioception, sometimes called the body's "sixth sense." It's what lets your brain track where your body is, how it's moving and how much force it's using without you having to think about it.

That sense depends on wiring laid down before birth, when the nervous system builds itself with astonishing precision. Some of the most important connections are made by commissural axons, which are nerve fibers that cross from one side of the developing spinal cord to the other, linking left and right so the two sides of the body can work together.

How do these fibers know exactly where to go? That question has occupied Dr. Guofa Liu, a professor in The University of Toledo's Department of Molecular, Cellular and Developmental Biology, for more than a decade.

"If these connections do not happen or are not properly formed, it can lead to significant neurological dysfunction," Liu said. "Because it's not just the spinal cord that has this kind of connection to our brain. It's the left side of the brain and the right side of the brain; they also have connections. These connections are robust."

Liu has received $560,925 in funding from the U.S. Department of Health and Human Services to continue his investigation into the molecular signals that guide those developing nerve fibers across the spinal cord's midline. His lab has identified two tiny molecular regulators called microRNAs, known as miR-219a and miR-92, that appear to function as a molecular switch controlling whether a nerve fiber crosses or stays put.

The consequences of those connections failing are visible in neurology every day. When stroke or spinal injury disrupts these circuits, patients often lose sensation or movement on the opposite side of their body, a hallmark of neurological damage that reflects just how precisely these crossings must be wired during development.

What Liu's lab discovered is that the two microRNAs, miR-92 and miR-219a, act like gatekeepers, helping control when growing nerve fibers are able to respond to signals that guide them across the spinal cord's midline. Before the nerve fibers reach the midline, the microRNAs keep a key receptor called Robo1 turned down, preventing the fibers from responding too early to signals that would push them away. That suppression allows the fiber to cross without being repelled too early. Once crossing is complete, the microRNAs step back, Robo1 levels rise and Slit repulsion kicks in, ensuring the axon stays on course rather than recrossing.

His lab has published research on both miR-92 in Molecular Biology of the Cell (MBoC) and miR-219a in iScience, establishing each molecule's role in this process in chicken and mouse models. The new federal funding will allow Liu's team to investigate how these two microRNAs work together and whether they regulate additional guidance receptors beyond Robo1, potentially uncovering broader mechanisms that govern other nervous system wiring.

"These molecular switches may control multiple receptors," Liu said. "During the process, we may identify new mechanisms. So, it is still an exploratory stage, and as we learn more, we may uncover additional mechanisms that control how these axons navigate."

The long-term implications extend beyond basic science.

MicroRNAs are increasingly of interest in medicine because they can be delivered into cells using technologies such as lipid nanoparticles, the same technology used in some vaccines, raising the possibility that correcting faulty microRNA signaling could one day become a therapeutic strategy for developmental neurological conditions. However, Liu emphasizes that any potential clinical application remains far in the future.

"RNAs can be packaged and delivered using lipid nanoparticles," Liu said. "In the future, RNA-based approaches could potentially be used to correct disease-associated pathways. But we need to know the mechanisms first, then find the next step toward translation."

That future is still a long way off, and Liu is careful to frame the current work as foundational. But the direction is clear: the immediate goal is to understand how molecular signals precisely coordinate guidance receptors during nervous-system development.

A defining feature of Liu's lab is its deliberate inclusion of undergraduate students in research that appears in peer-reviewed journals. Anagaa Nathan, now a first-year medical student at UToledo's College of Medicine and Life Sciences, contributed to the miR-219a study as an undergraduate co-author.

"The University of Toledo really encourages and supports students in their research endeavors and allows us to get involved in research as early as we would like to," Nathan said. "This experience, along with my research and clinical exposure, motivated me to pursue my education in this field so that I could better understand diseases that deeply impact both patients and their families."

That undergraduate research experience is just one of the ways UToledo delivers on the promise of the new experiential learning initiative, Applied Skills for Career Experience, Networking and Development (ASCEND), which makes applied learning a part of every new undergraduate's academic journey.
"It's our culture, undergraduate students do research in the research lab," Liu said. "This funding has one component for undergraduate education. You have to include the undergraduates in your grant proposal and in your research."